MOF (Metal Organic Framework) derivative catalyst for preparing methanol by hydrogenating carbon dioxide and preparation method of MOF derivative catalyst

Abstract

The invention belongs to the technical field of electro-catalysis, and relates to an MOF derivative catalyst for preparing methanol through hydrogenation of carbon dioxide and a preparation method of the MOF derivative catalyst. In order to solve the problems that an existing cobalt phthalocyanine catalyst is prone to aggregation, CO by-products poison active sites and the like, Zr-BTB MOF serves as a framework, a precursor is prepared through a solvothermal method, cobalt phthalocyanine and a heme unit are loaded in sequence, and then heat treatment activation is conducted under the protective atmosphere to prepare the series catalyst. In the catalyst, heme promotes CO2 to be converted into CO, cobalt phthalocyanine promotes CO to be hydrogenated to generate methanol, heme and cobalt phthalocyanine are spatially separated in MOF channels but are adjacently distributed, and efficient tandem catalysis is achieved. The Zr < 4 + > node of the Zr-BTB MOF can activate CO2, the pore structure of the Zr-BTB MOF inhibits the aggregation of active components, and the stability is enhanced. The catalyst can improve CO2 conversion rate, methanol selectivity and reaction efficiency, and is suitable for resource utilization of carbon dioxide.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalysis technology, and particularly relates to a MOF-derived catalyst for the hydrogenation of carbon dioxide to methanol and its preparation method. Background Technology

[0002] In recent years, the conversion of CO2 into high-value-added chemicals and fuels such as methanol, ethanol, gasoline, olefins, and aromatics has attracted widespread attention. Among these, methanol has received particular focus due to its excellent physicochemical properties. Methanol is both an important basic raw material for organic chemicals, ranking fourth globally in annual consumption, and a clean liquid fuel that is easy to store and transport. It can be used not only as a gasoline alternative in the automotive industry but also as fuel for fuel cell electric vehicles and other devices, or directly as a power source for methanol fuel cells. Furthermore, methanol has a C / H ratio of 1 / 4, making it suitable as a hydrogen carrier for hydrogen storage and transportation. Therefore, converting CO2 into methanol through hydrogenation can reduce CO2 emissions, effectively alleviate energy shortages, and contribute to sustainable economic and social development.

[0003] Traditional catalysts for the hydrogenation of CO2 to methanol are mainly based on copper-based or noble metal catalysts. Despite some progress, these catalysts still face challenges, such as the difficulty in balancing activity and selectivity, susceptibility to sintering and deactivation at high temperatures, and sensitivity to reaction conditions. In particular, due to the high thermodynamic stability and kinetic inertness of CO2 molecules, their activation typically requires high energy, leading to low reaction efficiency. Simultaneously, the reaction readily produces carbon monoxide byproducts, which not only reduces methanol selectivity but also causes CO molecules to strongly adsorb onto certain active sites, leading to catalyst poisoning and deactivation.

[0004] Molecular catalysts, particularly cobalt phthalocyanine (CoPc), have been extensively studied due to their well-defined active site structure, tunable electronic properties, and potential for catalytic CO2 reduction under mild conditions. CoPc can efficiently electrocatalyze the reduction of CO2 to CO. However, in practical applications, pure CoPc molecular catalysts have significant drawbacks: First, the strong π-π interactions between CoPc molecules lead to their easy stacking and aggregation in solution or on the support surface, thus masking a large number of active sites and severely reducing the accessibility of active sites and intrinsic catalytic activity. Second, in the multi-step reaction pathway of CO2 reduction to methanol, CO is a key intermediate. Although CoPc is adept at generating CO, the adsorption of CO intermediates by its active sites is often too strong, making it difficult for CO to be further hydrogenated to methanol. Instead, CO easily desorbs from the active sites and enters the system as a final byproduct. This CO poisoning effect severely limits the application of CoPc catalysts in the synthesis of higher-value products (such as methanol).

[0005] To overcome the aggregation problem of molecular catalysts, loading them onto supports with high specific surface area and ordered structures is an effective strategy. Metal-organic frameworks (MOFs), due to their ultra-high specific surface area, precisely tunable pore structure, abundant metal nodes, and organic connecting units, have become ideal platforms for immobilizing and dispersing molecular catalysts. Encapsulating or anchoring molecular catalysts such as CoPc within MOF channels can effectively suppress their aggregation by utilizing the confinement effect of MOFs, exposing more active sites. However, current research mainly focuses on using MOFs as single-function supports to disperse catalysts and improve the conversion efficiency from CO2 to CO. How to utilize the unique structure of MOFs to synergistically integrate active units with different catalytic functions to construct a highly efficient tandem catalytic system for the continuous conversion from CO2 to methanol still lacks in-depth exploration and effective material design strategies. In particular, how to precisely integrate CO2 activation sites, CO generation sites, and CO hydrogenation sites on the same MOF framework, and solve the problems of directional transport and efficient utilization of CO intermediates while avoiding their poisoning of CoPc sites, is currently a key technological bottleneck in this field. Summary of the Invention

[0006] In order to overcome the defects of CoPc catalyst stacking leading to a decrease in active sites and CO byproduct poisoning of CoPc in the prior art, this invention provides a novel MOF framework catalyst for the hydrogenation of carbon dioxide to methanol.

[0007] To achieve the above objectives, the following technical solution is adopted: On one hand, this invention provides a method for preparing a MOF-derived catalyst for the hydrogenation of carbon dioxide to methanol, comprising the following steps:

[0008] S1. Preparation of zirconium-containing metal-organic framework precursor: Zirconium salt, organic ligand 1,3,5-benzenetribenzoic acid and solvent are mixed and subjected to a solvothermal reaction. After the reaction is completed, the mixture is separated, washed and dried to obtain Zr-BTB MOF precursor;

[0009] S2. Preparation of CoPc functionalized MOF intermediate: The Zr-BTB MOF precursor obtained in step S1, cobalt phthalocyanine and the first solvent are mixed and a first mixing reaction is carried out to load cobalt phthalocyanine onto the pores or surface of the MOF through coordination or bonding. After the reaction is completed, the mixture is separated, washed and dried to obtain CoPc@MOF intermediate.

[0010] S3. Preparation of tandem catalyst: The CoPc@MOF intermediate obtained in step S2, heme, and the second solvent are mixed to carry out a second mixing reaction, so that the heme is loaded onto the pores or surface of the MOF through coordination or bonding. After the reaction is completed, the mixture is separated, washed, and dried to obtain the MOF-derived catalyst precursor.

[0011] S4. Activation treatment: Under a protective atmosphere, the catalyst precursor obtained in step S3 is subjected to heat treatment, and after cooling, the MOF-derived catalyst for the hydrogenation of carbon dioxide to methanol is obtained.

[0012] Among them, Zr-BTB MOFs possess high specific surface area, ordered pores, and tunable structure. Their stable zirconium cluster nodes and abundant coordination space provide an ideal support for CoPc and heme loading. This framework not only inhibits the stacking and aggregation of CoPc molecules, exposing more active sites, but also stabilizes the loaded active components through confinement effects, enhancing the overall stability of the catalyst. The MOF framework also exhibits certain electrical conductivity and electron transport capabilities, facilitating electron transfer between active sites.

[0013] Zr in the Zr-BTB MOF skeleton 4+ Zr is a typical Lewis acid site; its empty orbital can coordinate with the O atom (containing lone pair electrons) in the CO2 molecule, causing polarization and bond elongation, thus lowering the activation barrier of the CO2 molecule. This activation synergizes with the CO2-to-CO conversion function of the heme unit: Zr 4+ CO2 is first pre-activated to weaken the C=O bond strength, and then transferred to the Fe active center of heme for subsequent reduction, which significantly improves the kinetic rate of CO2 to CO conversion. At the same time, the pre-activated CO2 molecules are enriched in the MOF channels, further increasing the local CO2 concentration and providing sufficient substrate for the catalytic reaction of heme, thus forming a mechanism of pre-activation and efficient conversion.

[0014] The carboxyl group and pyrrole ring in the heme molecule possess proton-transfer capabilities, allowing them to capture protons in the reaction system and transfer them to the vicinity of the active site. On one hand, during the reduction of CO2 to CO, heme's proton-transfer function promotes proton participation in the reaction; on the other hand, protons not involved in CO formation can be transferred to the CoPc active site through the functional groups of heme, providing a sufficient proton source for CO hydrogenation, reducing diffusion resistance in the reaction system, and accelerating the overall hydrogenation process.

[0015] Further, in step S1, the zirconium salt is at least one of zirconium nitrate, zirconium sulfate, or zirconium acetate; the solvent is at least one of N,N-dimethylformamide, N,N-diethylformamide, or N,N-dimethylacetamide, or a mixture thereof with acetic acid and water.

[0016] Further, in step S1, the molar ratio of the zirconium salt to 1,3,5-benzenetribenzoic acid is 1:1 to 5:1; the temperature of the solvothermal reaction is 80-150℃, and the time is 12-72h.

[0017] Further, in step S2, the first solvent is at least one of N,N-dimethylformamide, dichloromethane, methanol, ethanol, and acetone; the reaction temperature of the first mixed reaction is 20-80℃, and the reaction time is 6-48h.

[0018] Further, in step S2, the mass ratio of the Zr-BTB MOF precursor to cobalt phthalocyanine is 1:1 to 10:1.

[0019] Further, the second solvent is at least one of N,N-dimethylformamide, methanol, ethanol, and water, or a mixture of them with a buffer salt solution; the reaction temperature of the second mixed reaction is 25-60°C, and the reaction time is 2-24 h.

[0020] Further, in step S3, the mass ratio of the CoPc@MOF intermediate to heme is 2:1 to 20:1.

[0021] Further, in step S4, the protective atmosphere is nitrogen, argon, or a mixture thereof; the temperature of the heat treatment is 200-500℃, the heating rate is 1-10℃ / min, and the holding time is 1-5h.

[0022] On the other hand, the present invention also provides a MOF-derived catalyst for the hydrogenation of carbon dioxide to methanol, which is prepared according to the preparation method described above.

[0023] Furthermore, the MOF-derived catalyst for the hydrogenation of carbon dioxide to methanol uses Zr-BTB MOF as a framework, with spatially separated cobalt phthalocyanine units and heme units simultaneously supported in its channels and / or on its surface to form a tandem catalytic system, wherein the heme units are used to promote the conversion of CO2 to CO, and the cobalt phthalocyanine units are used to promote the conversion of CO to CH3OH.

[0024] The beneficial effects of this invention are:

[0025] By constructing a MOF-based tandem system by installing CoPc and heme, an efficient electrochemical conversion of carbon dioxide to methanol can be achieved. Zr-BTB MOF has a regular and tunable pore structure, and its pore size matches the molecular size of CoPc and heme. When the two active units are encapsulated in the pores or anchored on the surface, the steric hindrance formed by the pore walls can not only avoid direct contact between CoPc molecules, but also inhibit the secondary aggregation of active components caused by molecular migration during the reaction, thus maintaining a high density of active sites in the long term.

[0026] Zr in MOF skeleton 4+Ions have abundant empty orbitals, which can form stable coordinate bonds with N atoms in CoPc molecules and N / O atoms in heme molecules, rather than simple physical adsorption. This strong interaction can effectively prevent the active components from falling off the MOF framework during the reaction, significantly improve the stability and lifespan of the catalyst during recycling, and avoid catalytic activity decay caused by the loss of active components.

[0027] Heme preferentially promotes the conversion of CO2 to CO, while CoPc promotes the hydrogenation of CO to CH3OH. The two are spatially separated but distributed in close proximity in the channels or on the surface of MOF, which allows CO intermediates to be rapidly transferred between active sites, thus connecting the reaction steps. This effectively reduces the diffusion loss of CO intermediates in the solution, increases the local CO concentration, alleviates the competitive adsorption problem of CO and CO2 on CoPc sites, and improves methanol selectivity and reaction efficiency. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of the MOF-derived catalyst of the present invention;

[0029] Figure 2 The results show the Faraday efficiency of methanol after electrolysis at different operating potentials according to this invention.

[0030] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0033] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the experimental materials used in the following examples are all purchased from commercial channels.

[0034] Example 1:

[0035] A method for preparing a MOF-derived catalyst for the hydrogenation of carbon dioxide to methanol includes the following steps:

[0036] S1. Preparation of zirconium-containing metal-organic framework precursor: Zirconium salt, organic ligand 1,3,5-benzenetribenzoic acid and solvent are mixed and subjected to a solvothermal reaction. After the reaction is completed, the mixture is separated, washed and dried to obtain Zr-BTB MOF precursor;

[0037] S2. Preparation of CoPc functionalized MOF intermediate: The Zr-BTB MOF precursor obtained in step S1, cobalt phthalocyanine and the first solvent are mixed and a first mixing reaction is carried out to load cobalt phthalocyanine onto the pores or surface of the MOF through coordination or bonding. After the reaction is completed, the mixture is separated, washed and dried to obtain CoPc@MOF intermediate.

[0038] S3. Preparation of tandem catalyst: The CoPc@MOF intermediate obtained in step S2, heme, and the second solvent are mixed to carry out a second mixing reaction, so that the heme is loaded onto the pores or surface of the MOF through coordination or bonding. After the reaction is completed, the mixture is separated, washed, and dried to obtain the MOF-derived catalyst precursor.

[0039] S4. Activation treatment: Under a protective atmosphere, the catalyst precursor obtained in step S3 is subjected to heat treatment, and after cooling, the MOF-derived catalyst for the hydrogenation of carbon dioxide to methanol is obtained.

[0040] In step S1, the zirconium salt is zirconium nitrate; the solvent is N,N-dimethylformamide; the molar ratio of the zirconium salt to 1,3,5-benzenetribenzoic acid in step S1 is 1:1; the solvothermal reaction temperature is 80℃ and the time is 12h; in step S2, the first solvent is N,N-dimethylformamide; the reaction temperature of the first mixed reaction is 20℃ and the reaction time is 6h; in step S2, the mass ratio of the Zr-BTB MOF precursor to cobalt phthalocyanine is 1:1; the second solvent is N,N-dimethylformamide; the reaction temperature of the second mixed reaction is 25℃ and the reaction time is 2h; in step S3, the mass ratio of the CoPc@MOF intermediate to heme is 2:1; in step S4, the protective atmosphere is nitrogen; the heat treatment temperature is 200℃, the heating rate is 1℃ / min, and the holding time is 1h.

[0041] Example 2:

[0042] A method for preparing a MOF-derived catalyst for the hydrogenation of carbon dioxide to methanol includes the same steps as in Example 1.

[0043] In step S1, the zirconium salt is zirconium acetate; the solvent is N,N-diethylformamide; the molar ratio of the zirconium salt to 1,3,5-benzenetribenzoic acid in step S1 is 5:1; the solvothermal reaction temperature is 150℃ and the time is 72h; in step S2, the first solvent is dichloromethane; the reaction temperature of the first mixed reaction is 80℃ and the reaction time is 48h; in step S2, the mass ratio of the Zr-BTB MOF precursor to cobalt phthalocyanine is 10:1; the second solvent is methanol; the reaction temperature of the second mixed reaction is 60℃ and the reaction time is 24h; in step S3, the mass ratio of the CoPc@MOF intermediate to heme is 20:1; in step S4, the protective atmosphere is argon; the heat treatment temperature is 500℃, the heating rate is 10℃ / min, and the holding time is 5h.

[0044] Example 3:

[0045] A method for preparing a MOF-derived catalyst for the hydrogenation of carbon dioxide to methanol includes the same steps as in Example 1.

[0046] In step S1, the zirconium salt is zirconium acetate; the solvent is N,N-dimethylacetamide; the molar ratio of the zirconium salt to 1,3,5-benzenetribenzoic acid in step S1 is 3:1; the solvothermal reaction temperature is 115℃ and the time is 42h. In step S2, the first solvent is methanol; the reaction temperature of the first mixed reaction is 50℃ and the reaction time is 27h; the mass ratio of the Zr-BTB MOF precursor to cobalt phthalocyanine in step S2 is 5:1; the second solvent is ethanol; the reaction temperature of the second mixed reaction is 42℃ and the reaction time is 13h. In step S3, the mass ratio of the CoPc@MOF intermediate to heme is 11:1. In step S4, the protective atmosphere is a mixture of nitrogen and argon in a volume ratio of 1:1; the heat treatment temperature is 350℃, the heating rate is 5℃ / min, and the holding time is 3h.

[0047] Comparative Example 1: In this comparative example, the CoPc@MOF intermediate obtained in step S2 was mixed with a second solvent without adding heme. The mixture was stirred, separated, washed, and dried at the same temperature and time as in Example 3 to obtain a catalyst precursor loaded only with cobalt phthalocyanine. The catalyst precursor was then heat-treated under a protective atmosphere and cooled to obtain the catalyst containing only CoPc.

[0048] Results Analysis

[0049] The Faradaic efficiency (FE) of methanol was measured after electrolysis of each catalyst at different operating potentials (vs. RHE). The results are shown in [Figure number missing]. Figure 2 .from Figure 2As can be seen, the tandem catalytic system constructed by integrating heme and CoPc through the MOF framework in this invention can efficiently and selectively reduce CO2 to methanol over a wide potential range, and its performance is far superior to that of single-component catalysts.

[0050] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0051] The present invention and its embodiments have been described above. This description is not restrictive, and the embodiments shown are only one of the embodiments of the present invention. The actual application is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar methods and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing a MOF-derived catalyst for the hydrogenation of carbon dioxide to methanol, characterized in that, Includes the following steps: S1. Preparation of zirconium-containing metal-organic framework precursor: Zirconium salt, organic ligand 1,3,5-benzenetribenzoic acid and solvent are mixed and subjected to a solvothermal reaction. After the reaction is completed, the mixture is separated, washed and dried to obtain Zr-BTB MOF precursor; S2. Preparation of CoPc functionalized MOF intermediate: The Zr-BTB MOF precursor obtained in step S1, cobalt phthalocyanine and the first solvent are mixed and a first mixing reaction is carried out to load cobalt phthalocyanine onto the pores or surface of the MOF through coordination or bonding. After the reaction is completed, the mixture is separated, washed and dried to obtain CoPc@MOF intermediate. S3. Preparation of tandem catalyst: The CoPc@MOF intermediate obtained in step S2, heme, and the second solvent are mixed to carry out a second mixing reaction, so that the heme is loaded onto the pores or surface of the MOF through coordination or bonding. After the reaction is completed, the mixture is separated, washed, and dried to obtain the MOF-derived catalyst precursor. S4. Activation treatment: Under a protective atmosphere, the catalyst precursor obtained in step S3 is subjected to heat treatment, and after cooling, the MOF-derived catalyst for the hydrogenation of carbon dioxide to methanol is obtained.

2. The method for preparing the MOF-derived catalyst for the hydrogenation of carbon dioxide to methanol according to claim 1, characterized in that: In step S1, the zirconium salt is at least one of zirconium nitrate, zirconium sulfate, or zirconium acetate; the solvent is at least one of N,N-dimethylformamide, N,N-diethylformamide, or N,N-dimethylacetamide, or a mixture thereof with acetic acid and water.

3. The method for preparing the MOF-derived catalyst for the hydrogenation of carbon dioxide to methanol according to claim 2, characterized in that: In step S1, the molar ratio of the zirconium salt to 1,3,5-benzenetribenzoic acid is 1:1 to 5:1; the temperature of the solvothermal reaction is 80-150℃ and the time is 12-72h.

4. The method for preparing the MOF-derived catalyst for the hydrogenation of carbon dioxide to methanol according to claim 3, characterized in that: In step S2, the first solvent is at least one of N,N-dimethylformamide, dichloromethane, methanol, ethanol, and acetone; the reaction temperature of the first mixed reaction is 20-80℃, and the reaction time is 6-48h.

5. The method for preparing the MOF-derived catalyst for the hydrogenation of carbon dioxide to methanol according to claim 4, characterized in that: In step S2, the mass ratio of the Zr-BTB MOF precursor to cobalt phthalocyanine is 1:1 to 10:

1.

6. The method for preparing the MOF-derived catalyst for the hydrogenation of carbon dioxide to methanol according to claim 5, characterized in that: The second solvent is at least one of N,N-dimethylformamide, methanol, ethanol, and water, or a mixture of them with a buffer salt solution; the reaction temperature of the second mixed reaction is 25-60°C, and the reaction time is 2-24 h.

7. The method for preparing the MOF-derived catalyst for the hydrogenation of carbon dioxide to methanol according to claim 6, characterized in that: In step S3, the mass ratio of the CoPc@MOF intermediate to heme is 2:1 to 20:

1.

8. The method for preparing the MOF-derived catalyst for the hydrogenation of carbon dioxide to methanol according to claim 7, characterized in that: In step S4, the protective atmosphere is nitrogen, argon, or a mixture thereof; the heat treatment temperature is 200-500℃, the heating rate is 1-10℃ / min, and the holding time is 1-5h.

9. A MOF-derived catalyst for the hydrogenation of carbon dioxide to methanol, characterized in that: Prepared by the method according to any one of claims 1-8.

10. The MOF-derived catalyst for the hydrogenation of carbon dioxide to methanol according to claim 9, characterized in that: The catalyst uses Zr-BTB MOF as a framework, and spatially separated cobalt phthalocyanine units and heme units are simultaneously loaded in its channels and / or on its surface to form a tandem catalytic system, wherein the heme units are used to promote the conversion of CO2 to CO, and the cobalt phthalocyanine units are used to promote the conversion of CO to CH3OH.

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